1. Field of the Invention
A method of reducing the Chemical Oxygen Demand (COD) of wastewater generated in the production of styrene-acrylonitrile copolymer (SAN) made by the suspension process. The method includes the step of treating the wastewater with a boric acid salt and a ferrous salt both being water soluble.
2. Description of the Prior Art:
In the manufacture of SAN by the suspension process, the monomers are charged into an aqueous mixture containing a suspending agent, usually polyvinyl alcohol. After the copolymer is recovered, the large amounts of polyvinyl alcohol and finely divided SAN particles remaining in the wastewater make pretreatment of the water very difficult.
U.S. Pat. No. 4,078,129 issued on Mar. 7, 1978 (Yamagata et al) describes a method of separating polyvinyl alcohol from solution by coagulating it with a "salting agent" and a salt of boric acid. The salting agent is defined as an inorganic salt of Group I or II metals, an inorganic ammonium salt or an inorganic aluminum salt. While the present invention does use a boric acid salt, it is used in conjunction with a ferrous salt (Group VIII) rather than the class of "salting agents" described in Yamagata et al.